Neural Tube Defects

Neural tube defects (NTDs) are birth defects of either the brain or spinal cord. This group of disorders is characterized by an opening in the brain or spinal cord occurring at an early stage of human development.

Incidence

NTDs are one of the most common birth defects.

Female predominance is observed. About 60-70% of all cases are females.

The incidence of neural tube disorders have fallen dramatically in recent years from 3 cases in every 1000 births to only 0.6 cases in every 1000 births.

Risk Factors

Cigarette smoking and maternal exposure to cigarette smoke

Maternal diabetes

Maternal obesity

Causes

Polygenic inheritance pattern

Poor maternal nutrition

Maternal diet deficient in folic acid

Intake of folate antimetabolites (methotrexate)

Use of teratogens

Review of the related anatomy and physiology

The central nervous system is the first observable structure in a human embryo. This embryo passes through 23 stages of development after conception. Two processes work in order to form the CNS:

Primary neurolation

Secondary neurolation

Primary neurolation is the formation of the neural structures into a tube. This forms the brain and the spinal cord. Secondary neurolation is the formation of the lower spinal cord. This gives rise to the lumbar and sacral elements.

Types of Neural Tube disorders

Anencephaly – absence of the cerebral hemispheres. Closure of the anterior neuropore occurs at stage 11 at about 23-26 days age of gestation. Failure of this point to close results to anencephaly. Children with this disorder cannot survive because of the absence of cerebral function. These children may only survive for a number days because the respiratory and cardiac centers are located in the intact medulla.

Microcephaly – characterized by a slow brain growth. Generally, infants with this disorder are cognitively challenged because of the lack of functioning brain tissue. The head circumference of affected neonates is decreased.

Spina Bifida Occulta – occurs when the posterior laminae of the vertebra fail to fuse at 26-28 days age of gestation. The most common site is the fifth lumbar or sacral level though it may occur at any point along the spinal canal.

Meningocele – herniation of the meninges through the unformed vertebrae of the spinal cord. Generally, it occurs at the lumbar area but it can be present anywhere along the spinal canal. It is characterized by an appearance of an orange-shaped mass at the center of the back.

Myelomeningocele – herniation of the spinal cord and meninges through the unformed vertebrae. The spinal cord ends at the pint of protrusion, thus, motor and sensory function beyond the point of herniation is absent.